The demand for high performance in advanced ULSI circuits requires a copper interconnect to carry high current density. This places severe challenges on copper interconnect reliability, especially concerning electromigration issues. Electromigration decreases the reliability of integrated circuits (ICs), with eventual loss of connections or failure of the circuit. Also, with increasing miniaturization, the probability of failure due to electromigration increases in very-large-scale integration (VLSI) and ultra-large-scale integration (ULSI) circuits because both the power density and the current density increase. Thus, as the structure size in ICs decreases, the practical significance of the electromigration effect increases.
In advanced semiconductor manufacturing processes, copper has replaced aluminum as the interconnect material of choice. Despite its greater fragility in the fabrication process, copper is intrinsically less susceptible to electromigration. However, electromigration continues to be an ever present challenge to device fabrication.
In dual damascene Cu interconnects, the via has been the weakest link for electromigration, especially for the via depletion mode, i.e., for electrons flowing from a dual damascene via upwards into a line. The common electromigration failure for this mode is void formation within the via. With the technology scaling, a void in the via needed to cause an electromigration failure becomes smaller, and consequently, the failure time becomes shorter.
Accordingly, there exists a need in the art to overcome the deficiencies and limitations described hereinabove.